That's well known, the question was: why? Why do D+ banner challenges only use "on disc" content? If someone has D+ access he's guaranteed to own certain cars and stages, so the events could use those.
Maybe you can get some more clarification on the "why" question.

It's not a bug, they somehow don't want your online My Team progress to be reset. Don't ask me why.
You can sell all cars. Buying and selling will lose you some money, so that should allow you to get close to 0 credits.

Same here. Screenshots, wrong position first, then after scrolling up:
https://steamcommunity.com/sharedfiles/filedetails/?id=1741301912
https://steamcommunity.com/sharedfiles/filedetails/?id=1741301951

I also have the impression that tyre wear has increased. That second run never would have "worn" the tyres before:
soft, Spain, 4.58+7.00+14.34km, 4WD2000cc Impreza: worn
soft, Spain, 10.75+6.55km, 4WD2000cc Impreza: worn
EDIT: and another run with worn tyres
soft, Australia, 12.50+6.89, R2 Opel: worn